Mechanism-based Pharmacokinetic/Pharmacodynamic Meta-analysis of Trabectedin (ET-743, Yondelis) Induced Neutropenia

Modeling approaches for reducing safety-related attrition in drug discovery and development: a review on myelotoxicity, immunotoxicity, cardiovascular toxicity, and liver toxicity

Introduction:Safety and tolerability is a critical area where improvements are needed to decrease the attrition rates during development of new drug candidates. Modeling approaches, when smartly implemented, can contribute to this aim.Areas covered:The focus of this review was on modeling approaches applied to four kinds of drug-induced toxicities: hematological, immunological, cardiovascular (CV) and liver toxicity. Papers, mainly published in the last 10 years, reporting models in three main methodological categories - computational models (e.g., quantitative structure-property relationships, machine learning approaches, neural networks, etc.), pharmacokinetic-pharmacodynamic (PK-PD) models, and quantitative system pharmacology (QSP) models - have been considered.Expert opinion:The picture observed in the four examined toxicity areas appears heterogeneous. Computational models are typically used in all areas as screening tools in the early stages of development for hematological, cardiovascular and liver toxicity, with accuracies in the range of 70-90%. A limited number of computational models, based on the analysis of drug protein sequence, was instead proposed for immunotoxicity. In the later stages of development, toxicities are quantitatively predicted with reasonably good accuracy using either semi-mechanistic PK-PD models (hematological and cardiovascular toxicity), or fully exploited QSP models (immuno-toxicity and liver toxicity).

Specific Effects of Trabectedin and Lurbinectedin on Human Macrophage Function and Fate-Novel Insights

BACKGROUND

Tumor-associated macrophages (TAMs) play a crucial role in suppressing the immunosurveillance function of the immune system that prevents tumor growth. Indeed, macrophages can also be targeted by different chemotherapeutic agents improving the action over immune checkpoints to fight cancer. Here we describe the effect of trabectedin and lurbinectedin on human macrophage cell viability and function.

METHODS

Blood monocytes from healthy donors were differentiated into macrophages and exposed to different stimuli promoting functional polarization and differentiation into tumor-associated macrophages. Cells were challenged with the chemotherapeutic drugs and the effects on cell viability and function were analyzed.

RESULTS

Human macrophages exhibit at least two different profiles in response to these drugs. One-fourth of the blood donors assayed (164 individuals) were extremely sensitive to trabectedin and lurbinectedin, which promoted apoptotic cell death. Macrophages from other individuals retained viability but responded to the drugs increasing reactive oxygen production and showing a rapid intracellular calcium rise and a loss of mitochondrial oxygen consumption. Cell-membrane exposure of programmed-death ligand 1 (PD-L1) significantly decreased after treatment with therapeutic doses of these drugs, including changes in the gene expression profile of hypoxia-inducible factor 1 alpha (HIF-1α)-dependent genes, among other.

CONCLUSIONS

The results provide evidence of additional onco-therapeutic actions for these drugs.

Gender medicine and oncology: report and consensus of an ESMO workshop

BACKGROUND

The importance of sex and gender as modulators of disease biology and treatment outcomes is well known in other disciplines of medicine, such as cardiology, but remains an undervalued issue in oncology. Considering the increasing evidence for their relevance, European Society for Medical Oncology decided to address this topic and organized a multidisciplinary workshop in Lausanne, Switzerland, on 30 November and 1 December 2018.

DESIGN

Twenty invited faculty members and 40 selected physicians/scientists participated. Relevant content was presented by faculty members on the basis of a literature review conducted by each speaker. Following a moderated consensus session, the final consensus statements are reported here.

RESULTS

Clinically relevant sex differences include tumour biology, immune system activity, body composition and drug disposition and effects. The main differences between male and female cells are sex chromosomes and the level of sexual hormones they are exposed to. They influence both local and systemic determinants of carcinogenesis. Their effect on carcinogenesis in non-reproductive organs is largely unknown. Recent evidence also suggests differences in tumour biology and molecular markers. Regarding body composition, the difference in metabolically active, fat-free body mass is one of the most prominent: in a man and a woman of equal weight and height, it accounts for 80% of the man's and 65% of the woman's body mass, and is not taken into account in body-surface area based dosing of chemotherapy.

CONCLUSION

Sex differences in cancer biology and treatment deserve more attention and systematic investigation. Interventional clinical trials evaluating sex-specific dosing regimens are necessary to improve the balance between efficacy and toxicity for drugs with significant pharmacokinetic differences. Especially in diseases or disease subgroups with significant differences in epidemiology or outcomes, men and women with non-sex-related cancers should be considered as biologically distinct groups of patients, for whom specific treatment approaches merit consideration.

Mathematical models for cytarabine-derived myelosuppression in acute myeloid leukaemia

We investigate the personalisation and prediction accuracy of mathematical models for white blood cell (WBC) count dynamics during consolidation treatment using intermediate or high-dose cytarabine (Ara-C) in acute myeloid leukaemia (AML). Ara-C is the clinically most relevant cytotoxic agent for AML treatment. We extend a mathematical model of myelosuppression and a pharmacokinetic model of Ara-C with different hypotheses of Ara-C's pharmacodynamic effects. We cross-validate the 12 model variations using dense WBC count measurements from 23 AML patients. Surprisingly, the prediction accuracy remains satisfactory in each of the models despite different modelling hypotheses. Therefore, we compare average clinical and calculated WBC recovery times for different Ara-C schedules as a successful methodology for model discrimination. As a result, a new hypothesis of a secondary pharmacodynamic effect on the proliferation rate seems plausible. Furthermore, we demonstrate the impact of treatment timing on subsequent nadir values based on personalised predictions as a possibility for influencing/controlling myelosuppression.

Trabectedin for inoperable or recurrent soft tissue sarcoma in adult patients: a retrospective cohort study

Background

Trabectedin is an antineoplastic agent used for patients with soft tissue sarcoma (STS) who fail standard-of-care treatment. Real-world data of its performance is scarce. This study evaluates the safety and effectiveness of trabectedin for patients with advanced STS who were treated at a high-volume sarcoma center.

Methods

A retrospective chart review was performed on 77 patients treated with trabectedin (24 h infusion q3w) between 01/2005 and 05/2014. Data regarding safety, objective radiological response, progression-free and overall survival were analyzed.

Results

Median age at treatment onset was 52y [interquartile range (IQR): 45-61y]. Tumors included leiomyosarcoma (41.6 %), liposarcoma (18.2 %), and synovial sarcoma (13 %). Trabectedin was provided as ≥ third-line chemotherapy in 71.4 %. Median number of cycles was 2 (range: 1–17). Dose reduction and treatment delays occurred in 19.5 and 40.3 %, respectively. Toxicities occurred in 78 %, primarily for neutropenia or elevated liver enzymes. Two patients died secondary to trabectedin-induced rhabdomyolysis. Treatment was discontinued because of disease progression (84.7 %), toxicity (10 %), and patient preference (5 %). Partial response or stable disease occurred in 14.1 and 33.8 %, respectively, while 52.1 % developed progressive disease. Median progression-free survival was 1.3 m (IQR: 0.7–3.5 m) and was significantly higher in patients lacking severe toxicities or progressive disease. Median overall survival was 6.7 m (IQR: 2.3–12.7 m) and was significantly higher in patients with leiomyosarcoma or liposarcoma relative to other histologies.

Conclusions

Trabectedin has an acceptable safety profile as an anti-tumor agent. Our data further suggest there may be some benefit in using trabectedin particularly in patients with leiomyo- or liposarcoma who failed standard-of-care agents.

Semimechanistic cell-cycle type-based pharmacokinetic/pharmacodynamic model of chemotherapy-induced neutropenic effects of diflomotecan under different dosing schedules

The current work integrates cell-cycle dynamics occurring in the bone marrow compartment as a key element in the structure of a semimechanistic pharmacokinetic/pharmacodynamic model for neutropenic effects, aiming to describe, with the same set of system- and drug-related parameters, longitudinal data of neutropenia gathered after the administration of the anticancer drug diflomotecan (9,10-difluoro-homocamptothecin) under different dosing schedules to patients (n = 111) with advanced solid tumors. To achieve such an objective, the general framework of the neutropenia models was expanded, including one additional physiologic process resembling cell cycle dynamics. The main assumptions of the proposed model are as follows: within the stem cell compartment, proliferative and quiescent cells coexist, and only cells in the proliferative condition are sensitive to drug effects and capable of following the maturation chain. Cell cycle dynamics were characterized by two new parameters, FProl (the fraction of proliferative [Prol] cells that enters into the maturation chain) and kcycle (first-order rate constant governing cell cycle dynamics within the stem cell compartment). Both model parameters were identifiable as indicated by the results from a bootstrap analysis, and their estimates were supported by date from the literature. The estimates of FProl and kcycle were 0.58 and 1.94 day(-1), respectively. The new model could properly describe the neutropenic effects of diflomotecan after very different dosing scenarios, and can be used to explore the potential impact of dosing schedule dependencies on neutropenia prediction.

Trabectedin: Supportive care strategies and safety profile

Trabectedin is an approved antineoplastic agent for the treatment of adult patients with advanced soft tissue sarcomas or in combination with pegylated liposomal doxorubicin (PLD) in patients with relapsed platinum sensitive ovarian cancer. The mechanism of action is still not fully understood but many typical side effects seen with other chemotherapy drugs are less common, mild or unreported. Although this apparent favorable safety profile suggests a well-tolerated and manageable therapeutic option in the palliative care setting, trabectedin does have specific adverse side effects which can be hazardous for individual patients. The most commonly observed toxicities with trabectedin include neutropenia, nausea, vomiting, and increases in liver transaminases, anemia, fatigue, thrombocytopenia, anorexia and diarrhea. However, for most patients the appropriate use of supportive care strategies can reduce or overcome these side effects. We present a concise review of the safety data of trabectedin with the corresponding overview of the supportive care strategies.

Clinical Trial Simulation to Inform Phase 2: Comparison of Concentrated vs. Distributed First-in-Patient Study Designs in Psoriasis

Clinical trial simulation (CTS) and model-based meta-analysis (MBMA) can increase our understanding of small, first-in-patient (FIP) trial design performance to inform Phase 2 decision making. In this work, we compared dose-ranging designs vs. designs testing only placebo and the maximum dose for early decision making in psoriasis. Based on MBMA of monoclonal antibodies in the psoriasis space, a threshold of greater than a 50 percentage point improvement over placebo effect at the highest feasible drug dose was required for the advancement in psoriasis. Studies testing only placebo and the maximum dose made the correct advancement decision marginally more often than dose-ranging designs in the majority of the cases. However, dose-ranging studies in FIP trials offer important design advantages in the form of dose–response (D–R) information to inform Phase 2 dose selection. CTS can increase the efficiency and quality of drug development decision making by studying the limitations and benefits of study designs prospectively.

Population pharmacokinetic–pharmacodynamic modelling and simulation of neutropenia induced by TP300, a novel topoisomerase I inhibitor

Objectives

TP300 is a novel topoisomerase I inhibitor with neutropenia as a significant toxicity. We developed and evaluated a pharmacokinetic–pharmacodynamic (PK-PD) model, using data from Phase I and II trials to predict neutrophil decrease in patients treated with TP300.

Methods

Plasma drug concentrations of TP300, its active form TP3076 and active metabolite TP3011 and absolute neutrophil counts (ANCs) from a Phase I trial were analysed as a training dataset. A two-plus-two-compartment model was applied to the pharmacokinetics of TP3076 and TP3011. A semi-mechanistic model was used to describe the PK-PD relationship between the plasma concentration of TP3076 and TP3011, and changes in ANC.

Key findings

 The model fitted well to plasma concentrations of TP3076 and TP3011. Model appropriateness was confirmed in a Phase II trial validation dataset. Body weight and liver biochemistry values were identified as covariates. A semi-mechanistic PK-PD model was applied and the longitudinal decrease in ANC was simulated. Neutrophil counts reached their nadir approximately 2 weeks after administration of TP300, and the proportion of subjects affected increased with dose.

Conclusions

This PK-PD model to predict neutropenia following treatment with TP300 fitted well the decrease in ANC with total concentration of TP3076 and TP3011.

Population pharmacokinetic/pharmacodynamic modeling of drug-induced adverse effects of a novel homocamptothecin analog, elomotecan (BN80927), in a Phase I dose finding study in patients with advanced solid tumors

PURPOSE

To characterize the pharmacokinetic profile of elomotecan, a novel homocamptothecin analog, evaluate the dose-limiting toxicities, and establish the relationship between exposure and toxicity in the first Phase I study in patients with advanced malignant solid tumors. Preliminary antitumor efficacy results are also provided.

DESIGN

Elomotecan was administered as a 30-min intravenous infusion at doses ranging from 1.5 to 75 mg once every 3 weeks to 56 patients with advanced solid tumors. Plasma concentration data and adverse effects were modeled using the population approach.

RESULTS

Elomotecan showed linear pharmacokinetics, and clearance was decreased with age. The model predicts a 47 and 61 % reduction in CL for patients aged 60 and 80 years, respectively, when compared with younger patients (30 years). Neutropenia represented the dose-limiting toxicity. The maximum tolerated dose and the recommended dose (RD) were 75 and 60 mg, respectively. Elomotecan elicited a 20, 5, 2, and 2 % severe (grade 4) neutropenia, asthenia, nausea, and vomiting at the RD, respectively. Of the subjects in the RD cohort, 41.7 % had a stable disease mean duration of 123.6 ± 43.4 days.

CONCLUSIONS

The pharmacokinetic parameters and the toxicity pattern of elomotecan suggest that this novel homocamptothecin analog should be further explored in the clinical setting using a dose of 60 mg administered as a 30-min intravenous infusion, once every 3 weeks.

Quantitative model of the relationship between dipeptidyl peptidase-4 (DPP-4) inhibition and response: meta-analysis of alogliptin, saxagliptin, sitagliptin, and vildagliptin efficacy results

Dipeptidyl peptidase-4 (DPP-4) inhibition is a well- characterized treatment for type 2 diabetes mellitus (T2DM). The objective of this model-based meta-analysis was to describe the time course of HbA1c response after dosing with alogliptin (ALOG), saxagliptin (SAXA), sitagliptin (SITA), or vildagliptin (VILD). Publicly available data involving late-stage or marketed DPP-4 inhibitors were leveraged for the analysis. Nonlinear mixed-effects modeling was performed to describe the relationship between DPP-4 inhibition and mean response over time. Plots of the relationship between metrics of DPP-4 inhibition (ie, weighted average inhibition [WAI], time above 80% inhibition, and trough inhibition) and response after 12 weeks of daily dosing were evaluated. The WAI was most closely related to outcome, although other metrics performed well. A model was constructed that included fixed effects for placebo and drug and random effects for intertrial variability and residual error. The relationship between WAI and outcome was nonlinear, with an increasing response up to 98% WAI. Response to DPP-4 inhibitors could be described with a single drug effect. The WAI appears to be a useful index of DPP-4 inhibition related to HbA1c. Biomarker to response relationships informed by model-based meta-analysis can be leveraged to support study designs including optimization of dose, duration of therapy, and patient population.

Natural products synthesis: enabling tools to penetrate Nature's secrets of biogenesis and biomechanism

Selected examples from our laboratory of how synthetic technology platforms developed for the total synthesis of several disparate families of natural products was harnessed to penetrate biomechanistic and/or biosynthetic queries is discussed. Unexpected discoveries of biomechanistic reactivity and/or penetrating the biogenesis of naturally occurring substances were made possible through access to substances available only through chemical synthesis. Hypothesis-driven total synthesis programs are emerging as very useful conceptual templates for penetrating and exploiting the inherent reactivity of biologically active natural substances. In many instances, new enabling synthetic technologies were required to be developed. The examples demonstrate the often untapped richness of complex molecule synthesis to provide powerful tools to understand, manipulate and exploit Nature's vast and creative palette of secondary metabolites.

Pharmacokinetic and pharmacodynamic analysis of hyperthermic intraperitoneal oxaliplatin-induced neutropenia in subjects with peritoneal carcinomatosis

The objective of this study was to characterize the pharmacokinetics and the time course of the neutropenia-induced by hyperthermic intraperitoneal oxaliplatin (HIO) after cytoreductive surgery in cancer patients with peritoneal carcinomatosis. Data from 30 patients who received 360 mg/m(2) of HIO following cytoreductive surgery were used for pharmacokinetic-pharmacodynamic (PK/PD) analysis. The oxaliplatin plasma concentrations were characterized by an open two-compartment pharmacokinetic model after first-order absorption from peritoneum to plasma. An oxaliplatin-sensitive progenitor cell compartment was used to describe the absolute neutrophil counts in blood. The reduction of the proliferation rate of the progenitor cells was modeled by a linear function of the oxaliplatin plasma concentrations. The typical values of oxaliplatin absorption and terminal half-lives were estimated to be 2.2 and 40 h, with moderate interindividual variability. Oxaliplatin reduced the proliferation rate of the progenitor cells by 18.2% per mg/L. No patient's covariates were related to oxaliplatin PK/PD parameters. Bootstrap and visual predictive check evidenced the model was deemed appropriate to describe oxaliplatin pharmacokinetics and the incidence and severity of neutropenia. A peritoneum oxaliplatin exposure of 65 and 120 mg·L/h was associated with a 20% and 33% incidence of neutropenia grade 4. The time course of neutropenia following HIO administration was well described by the semiphysiological PK/PD model. The maximum tolerated peritoneum oxaliplatin exposure is 120 mg L/h and higher exposures should be avoided in future studies. We suggest the prophylactic use of granulocyte colony stimulating factor for patients treated with HIO exposure higher than 65 mg L/h.

Semi-mechanistic population pharmacokinetic/pharmacodynamic model for neutropenia following therapy with the Plk-1 inhibitor BI 2536 and its application in clinical development

PURPOSE

(1) To describe the neutropenic response of BI 2536 a polo-like kinase 1 inhibitor in patients with cancer using a semi-mechanistic model. (2) To explore by simulations (a) the neutropenic effects for the maximum tolerated dose (MTD) and the dose at which dose-limiting toxicity occurred, (b) the possibility to reduce the cycle duration without increasing neutropenia substantially, and (c) the impact of the initial absolute neutrophil count (ANC) on the degree of neutropenia for different doses.

EXPERIMENTAL DESIGN

BI 2536 was administered as intravenous infusion over 60 min in the dose range from 25 to 250 mg. Three different administration schedules were explored: (a) day 1, (b) days 1, 2, and 3 or (c) days 1 and 8 within a 3 week treatment cycle. BI 2536 plasma concentrations and ANC obtained during the first treatment cycle from 104 patients were analysed using the population approach with NONMEM VI.

RESULTS

Neutropenia was described by a semi-mechanistic model resembling proliferation at the stem cell compartment, maturation, degradation, and homeostatic regulation. BI 2536 acts decreasing proliferation rate. Simulations showed that (1) all MTD doses showed an acceptable risk of neutropenia, (2) when BI 2536 is given as 200 mg single administration, cycle duration can be reduced from 3 to 2 weeks, and (3) baseline ANC might be considered to individualise the dose of BI 2536.

CONCLUSIONS

A semi-mechanistic population model was applied to describe the neutropenic effects of BI 2536. The model was used for simulations to support further clinical development.

Trabectedin: the evidence for its place in therapy in the treatment of soft tissue sarcoma

INTRODUCTION

Soft tissue sarcoma accounts for less than 1% of all malignant neoplasms and is comprised of a very heterogeneous group of tumors with over 50 different subtypes. Due to its diversity and rarity, developing new therapeutics has been difficult, at best. The standard of care in the treatment of advanced and metastatic disease over the last 30 years has been doxorubicin and ifosfamide, either alone or in combination. There has been significant focus on developing new therapeutics to treat primary and metastatic disease. Trabectedin (ecteinascidin-743) is a tetrahydroiso-quinoline alkaloid which has been evaluated in the treatment of metastatic soft tissue sarcoma.

AIMS

To review the current evidence for the therapeutic use of trabectedin in patients with soft tissue sarcoma.

EVIDENCE REVIEW

Five phase I studies in patients with solid tumors, all of which include sarcoma patients, evaluating the dosing and toxicity of trabectedin were performed with efficacy being evaluated as a secondary endpoint. Additionally, there are four phase I trials evaluating trabectedin in combination with frontline therapeutic drugs in soft tissue sarcoma. Four phase II studies were performed in soft-tissue sarcoma patients with objective response rates ranging from 3.7% to 17.1%. Additionally, in two compassionate use trials, objective response rates between 14% and 51% were seen, the largest response resulting from a study specifically focusing on liposarcoma.

PLACE IN THERAPY

Trabectedin is a potential therapeutic option for the management of soft-tissue sarcoma. It appears to have specific activity in a select group of histologies, most notably myxoid/round cell liposarcoma. Although it would be helpful to study the use of trabectedin in a randomized, controlled fashion, the relative rarity of soft-tissue sarcoma, and heterogeneity of the histologic subtypes, makes phase III trials a difficult prospect.

Wide-spectrum characterization of trabectedin: biology, clinical activity and future perspectives

Ecteinascidin-743 (trabectedin, Yondelis®; PharmaMar, Madrid, Spain), a 25-year-old antineoplastic alkylating agent, has recently shown unexpected and interesting mechanisms of action. Trabectedin causes perturbation in the transcription of inducible genes (e.g., the multidrug resistance gene MDR1) and interaction with DNA repair mechanisms (e.g., the nucleotide excision repair pathway) owing to drug-related DNA double strand breaks and adduct formation. Trabectedin was the first antineoplastic agent from a marine source (namely, the Caribbean tunicate Ecteinascidia turbinata) to receive marketing authorization. This article summarizes the mechanisms of action, the complex metabolism, the main toxicities, the preclinical and clinical evidences of its antineoplastic effects in different types of cancer and, finally, the future perspectives of this promising drug.

Semi-mechanistic model for neutropenia after high dose of chemotherapy in breast cancer patients

PURPOSE

To describe the absolute neutrophil counts (ANC) profile in breast cancer patients receiving high-dose of chemotherapy and peripheral blood stem-cells (PBSC) transplantation.

METHODS

Data from 41 subjects receiving cyclophosphamide, thiotepa and carboplatin were used to develop the ANC model consisting of a drug-sensitive progenitor cell compartment, linked to the peripheral blood compartment, through three transition compartments. PBSC were incorporated into the first transit compartment following a zero-order process, k(in), and the rebound effect was explained by a feedback mechanism. A 'kinetics of drug action' model was used to quantify the HDC effect on the progenitor cells according to a linear function, with a slope (alpha).

RESULTS

The typical of the ANC at baseline (Circ(0)), mean transit time (MTT), feedback parameter (gamma), k(in) and alpha were estimated to be 5,610 x 10(6)/L, 3.25 days, 0.145, 0.954 cell/kg/day and 2.50 h/U, respectively. rHuG-CSF shortens the MTT by 92% and increases the mitotic activity by 120%. Bootstrap analysis, visual predictive check and numerical predictive checks evidenced accurate prediction of the ANC nadir, time to ANC nadir and time to grade 4 neutropenia recovery.

CONCLUSION

The time course of neutropenia following high-dose of chemotherapy and PBSC transplantation was accurately predicted. Higher amount of CD34+ cells in the PBSC transplantation and earlier administration rHuG-CSF were associated with faster haematological recovery.

Multiple-pool cell lifespan models for neutropenia to assess the population pharmacodynamics of unbound paclitaxel from two formulations in cancer patients

PURPOSE

Our objective was to build a mechanism-based pharmacodynamic model for the time course of neutropenia in cancer patients following paclitaxel treatment with a tocopherol-based Cremophor-free formulation (Tocosol Paclitaxel) and Cremophor EL-formulated paclitaxel (Taxol).

METHODS

A randomized two-way crossover trial was performed with 35 adult patients who received 175 mg/m(2) paclitaxel as either 15 min (Tocosol Paclitaxel) or 3 h (Taxol) intravenous infusions. Paclitaxel concentrations were measured by LC-MS/MS. NONMEM VI was used for population pharmacodynamics.

RESULTS

The cytotoxic effect on neutrophils was described by four mechanism-based models predicated on known properties of paclitaxel that used unbound concentrations in the central, deep peripheral or an intracellular compartment as forcing functions. Tocosol Paclitaxel was estimated to release 9.8% of the dose directly into the deep peripheral compartment (DPC). All models provided reasonable fitting of neutropenic effects. The model with the best predictive performance assumed that this dose fraction was released into 22.5% of the DPC which included the site of toxicity. The second-order cytotoxic rate constant was 0.00211 mL/ng per hour (variability: 52% CV). The relative exposure at the site of toxicity was 2.21 +/- 0.41 times (average +/- SD) larger for Tocosol Paclitaxel compared to Taxol. Lifespan was 11.0 days for progenitor cells, 1.95 days for maturating cells, and 4.38 days for neutrophils. Total drug exposure in blood explained half of the variance in nadir to baseline neutrophil count ratio.

CONCLUSIONS

The relative exposure of unbound paclitaxel at the site of toxicity was twice as large for Tocosol Paclitaxel compared to Taxol. The proposed mechanism-based models explained the extent and time course of neutropenia jointly for both formulations.